The phrase "a large army of" is correct and usable in written English.
It can be used when describing a significant number of people or entities that are organized for a common purpose, often in a military or metaphorical context.
Example: "The kingdom was defended by a large army of brave soldiers ready to fight for their homeland."
Alternatives: "a vast number of" or "a significant force of".
A large army of devoted players can sweep over an opponent's territory with ease.
He also insisted on using a large army of climbers who worked methodically as a team.
Unlike the F.S.I.S., the F.D.A. does not have a large army of inspectors for the products under its purview.
Instead of a large army of ward heelers dragging people to the polls, candidates needed a small army of donors to pay for commercials.
The race is considered competitive because the two challengers had respectable showings two years ago and both have a large army of campaign volunteers.
First he turned against a large army of the Mushki that had entered into southern Armenia from Anatolia, defeating them decisively.
If he was part of a larger army of innovators responding to the progressive taste of the time and reshaping opera for the 21st century, he was certainly a general in that army.
As a result of his (and Suger's) appeal to the nobility's veneration for the saint, he was followed by a larger army of nobles than had ever previously pledged their allegiance to him or to his father.
The army of Carthage, under Hannibal, decisively defeated a larger army of the Roman Republic, under the consuls Lucius Aemilius Paullus and Gaius Terentius Varro.
To these ends, Nādir Shah built up a large army composed of tribal units under their own chiefs, such as his Afshārid kinsmen and the Qājār and Bakhtyārī.
In response, Samuel sent a large army under one of the most able Bulgarian nobles, Nestoritsa, to strike southwards and draw the attention of Basil away from the siege at Klyuch.
